perf_event: on old kernels if SW Multiplex enabled, then report proper number of MPX counters available
perf_event: on old kernels if SW Multiplex enabled, then report proper
number of MPX counters available

it may be different than the amount HW supports

pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi